1. Field of the Invention
This invention relates generally to improvements to trailer jacks and particularly to release mechanisms for trailer jacks which permit quick vertical shifting of the support leg, or mast, to avoid time consuming cranking necessary with conventional jacks.
2. Description of Related Art
Jacks for trailer tongues long have been available to support the weight of the tongue while the trailer is parked or when coupling it to a towing vehicle. Such jacks usually comprise a body having a cylindrical silo through which a support mast extends both above and below the tongue. The mast terminates in some type of footing, usually a wheel, and a rack gear extends along one side substantially the length of the mast. Within the jack body, a series of gears couples a crank handle to the rack gear to assist an operator in raising or lowering the mast under the load of the trailer tongue. This gear reduction system provides the operator a mechanical advantage that limits the force necessary to crank the handle by increasing the required number of rotations of the crank.
In preparation for towing, the mast must be cranked vertically upward to lift its foot out of the way of ground obstacles. Such activity conventionally involves cranking the mast a substantial portion of its length. This is due to the fact that the mast is fully extended to the ground to support the tongue at the hitch height, and the fact that it must be retracted fully to avoid all road obstacles. Absent some release mechanism to decouple the mast from the gear reduction system, however, the same number of rotations of the crank handle are necessary to move the unloaded mast as are required to move the loaded mast. Such cranking thus requires a substantial amount of time to raise and lower the mast. A need therefore exists for a means of mitigating the time necessary to raise and lower the support mast when it does not carry the load of the tongue.
Numerous devices provide a means of decoupling a portion of the gear reduction system to permit the mast to move free thereof, allowing an operator to lift or drop the mast quickly to a preferred vertical position while the system is disengaged. Kendrick, U.S. Pat. No. 4,702,458, provides a channel in which the rack gear travels that is wide enough to permit the rack gear to rotate axially and to decouple from the pinion drive gear. A retaining block must be lifted out of the way to permit the mast to rotate. Though simple in its design, Kendrick requires that the mast be free not only to shift vertically when lifted, but also to rotate axially, requiring the operator to move it rather precisely and simultaneously in two different dimensions. Gipson, U.S. Pat. No. 4,978,104, provides a spring loaded lever which decouples the drive pinion gear from the rack by moving it in a direction radial to the mast and away from the rack when a lever is depressed. Though the movements required of the operator are simple, Gipson involves multiple levers and moving parts which complicate the jack mechanism and increase its cost and risk of malfunction. A need exists for a simple and inexpensive mechanism which overcomes the shortcomings of these and other prior art devices.